Predicting Ionic Solubility Precipitation Formation.

Predicting Ionic Solubility

Precipitation Formation


Most Ionic compounds (Salts) are soluble in water, but the degree of solubility is different for different salts. Salts can be described in one of the following categories:

SolublePartly (or Sparingly) SolubleInsoluble


A soluble salt can be defined in 2 ways: Qualitatively:

Soluble salts tend to dissolve in aqueous solution in almost unlimited amounts.

Quantitatively:More than 1 g of the salt dissolves in 100 mL of solution. or More than 0.1 mole of the salt will dissolve in 1 L of

solution.


A partly soluble salt can be defined in 2 ways: Qualitatively:

Partly soluble salts tend to dissolve in aqueous solution but in limited amounts.

Quantitatively:Between 1 g and 0.1g of the salt dissolves in 100 mL of

solution. Between 0.1mole and 0.01 mole of the salt will dissolve in 1 L

of solution.


An insoluble salt can be defined in 2 ways: Qualitatively:

Insoluble salts do not dissolve in aqueous solution in any amount.

Quantitatively:Less than 0.1g of the salt dissolves in 100 mL of solution. Less than 0.01 mole of the salt will dissolve in 1 L of solution.

Predicting Solubility - Using the Solubility Chart

Using the Solubility Chart, a guided example.Example: Is Calcium carbonate soluble or

insoluble?1. Determine the ions present in this

compound: - Ca2+ and CO32-

2. Look up the anion on the Solubility chart. (in this case CO3

2-)1. Look for the cation (in this case Ca2+) in

the two lists: if the combination of Ca2+ and CO3

2-

forms a precipitate, the chart will indicate it is insoluble or

has low solubility. if the combination of Ca2+ and CO3

2-

doesn’t form a precipitate, the chart will indicate it is soluble.


Using the Solubility Chart, a guided example.

Example: Is Calcium carbonate soluble or insoluble?

1. Determine the ions present in this compound:




2-



2-





1. Determine the ions present in this compound: - Ca2+ and CO3

2-




2-



2-






2-



the two lists:• is the combination of Ca2+ and CO3

2- in the soluble group?

1. is the combination of Ca2+ and CO32- in

the insoluble group? if the combination of Ca2+ and CO3

2-






2-



the two lists:• is the combination of Ca2+ and CO3

2- in the soluble group? NO


the insoluble group?2. if the combination of Ca2+ and CO3

2-






2-



the two lists:1. is the combination of Ca2+ and CO3



the insoluble group? if the combination of Ca2+ and CO3

2-






2-






the insoluble group? YES 3. if the combination of Ca2+ and CO3

2-






2-






the insoluble group? The combination of Ca2+ and CO3

2-

forms a precipitate, the chart indicates it has Low Solubility


Use a solubility chart to predict the solubility of the following compounds in water. State whether they are soluble or insoluble in water.

Ca(NO3)2 CuCl2

KBr (NH4)2CO3

Fe(NO3)3 Ca(OH)2

NH4CH3COO Pb(NO3)4

Ca3(PO4)2 CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3



Ca(NO3)2 soluble CuCl2

KBr (NH4)2CO3

Fe(NO3)3 Ca(OH)2

NH4CH3COO Pb(NO3)4

Ca3(PO4)2 CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3




KBr soluble (NH4)2CO3

Fe(NO3)3 Ca(OH)2

NH4CH3COO Pb(NO3)4

Ca3(PO4)2 CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3





Fe(NO3)3 soluble Ca(OH)2

NH4CH3COO Pb(NO3)4

Ca3(PO4)2 CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3






NH4CH3COO soluble Pb(NO3)4

Ca3(PO4)2 CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3







Ca3(PO4)2 insoluble CuCl

KCH3COO PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3








KCH3COO soluble PbCO3

BaSO4 AgOH

Ag2SO4 Cr(OH)3









BaSO4 insoluble AgOH

Ag2SO4 Cr(OH)3










Ag2SO4 insoluble Cr(OH)3



Ca(NO3)2 soluble CuCl2 soluble











KBr soluble (NH4)2CO3 soluble











Fe(NO3)3 soluble Ca(OH)2 insoluble











NH4CH3COO soluble Pb(NO3)4 soluble











Ca3(PO4)2 insoluble CuCl insoluble











KCH3COO soluble PbCO3 insoluble











BaSO4 insoluble AgOH insoluble










BaSO4 insoluble AgOH insoluble

Ag2SO4 insoluble Cr(OH)3 insoluble

General Solubility Rules (Time savers)

Nitrates (NO31-)

soluble with all cations.

Ammonium (NH41+)

soluble with all anions.

Alkali Metals (Li1+, Na1+, K1+,…)soluble with all anions.

Predicting the Precipitate that Forms in a Chemical Reaction

In a chemical reaction between two Ionic solutions, a precipitate may form.

If a precipitate forms, one of the products of the reaction is the precipitate, in other words, it is insoluble and it is a solid.

We can predict which product forms the precipitate if we have a solubility chart handy.


For example, When a solution of Potassium iodide [KI (aq)] reacts with a

solution of Lead (II) nitrate [Pb(NO3)2 (aq)], a yellow precipitate forms.

This reaction can be described in words: Potassium iodide solution reacts with Lead (II) nitrate

solution to form Potassium nitrate with Lead (II) iodide. One of the products is insoluble (the yellow precipitate)


First Step: Write out the Balanced Reaction Equation:

2KI (aq) + 1Pb(NO3)2(aq) 2KNO3(?) + 1PbI2(?)

Second step: Determine which product is insoluble:

Name of product Formula Solubility

Potassium nitrate

Lead (II) iodide






Potassium nitrate KNO3

Lead (II) iodide PbI2






Potassium nitrate KNO3 Soluble - ie (aq)

Lead (II) iodide PbI2






Potassium nitrate KNO3 Soluble - ie (aq)

Lead (II) iodide PbI2 Insoluble - ie (s)


The Total Ionic Equation shows all of the ions present in the two solutions, and which ones form the precipitate. When writing this equation, you must balance the atoms and the charges, you must also indicate which species are (aq) and which, if any forms the precipitate (s).

2K1+(aq) + 2I1-

(aq)



2K1+(aq) + 2I1-

(aq) + 1Pb2+(aq) + 2NO3

1- (aq)



2K1+(aq) + 2I1-

(aq) + 1Pb2+(aq) + 2NO3

1- (aq) 2K1+

(aq) + 2NO31-

(aq)



2K1+(aq) + 2I1-

(aq) + 1Pb2+(aq) + 2NO3

1- (aq) 2K1+

(aq) + 2NO31-

(aq) + 1PbI2(s)


The Net Ionic Equation demonstrates only the ions that form the precipitate. To show the Net Ionic Equation, you get rid of Spectator Ions – ions that do not take part in the reaction (ie., they appear the

same on the reactant side as they do on the product side.)

2K1+(aq) + 2I1-

(aq) + 1Pb2+(aq) + 2NO3

1- (aq) 2K1+

(aq) + 2NO31-

(aq) + 1PbI2(s)


The Net Ionic Equation demonstrates only the ions that form the precipitate. To show the Net Ionic Equation, you get rid of Spectator Ions – ions that do not take part in the reaction (ie., they appear the

same on the reactant side as they do on the product side.)

Simplified and rearranged:

1Pb2+(aq) + 2I1-

(aq) 1PbI2(s)

Summary - Big Ideas

Some double displacement reactions form precipitates.

Precipitates form in double displacement reactions between two ionic solutions.

Precipitates are insoluble ionic compounds, and do not dissolve.

A net ionic equation demonstrates only the ions that react.

Any Questions?

Predicting Ionic Solubility Precipitation Formation.

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